Access systems generally provide access to restricted means, such as communication systems and data, or to restricted areas such as buildings and departments. There are known in the art access systems which employ integrated circuit (IC) cards, or as more commonly referred to "smart cards", to provide secure access to restricted means or areas.
Smart cards are employed in systems such as pay TV systems and telephone systems. Such systems generally employ one card per unit which is to be accessed, whereby access is enabled whenever a valid smart card is inserted in a card slot.
U.S. Pat. No. 4,709,136 to Watanabe describes an IC card reader/writer apparatus which includes at least two contactors in which IC cards are inserted, respectively, card detecting means for detecting that at least two IC cards have been loaded, and collating means verifying that correct cipher codes of the two IC cards coincide with those inputted externally, respectively, wherein access to the contents stored in the IC cards is allowed only when the collation results in coincidence.
U.S. Pat. No. 4,594,663 to Nagata et al describes a credit transaction processing system which processes data related to a commodity entered into by using a card owned by a customer and a recording card owned by a store.
U.S. Pat. No. 5,010,571 to Katznelson describes a system for controlling and accounting for retrieval of data from a CD-ROM memory containing encrypted data files from which retrieval must be authorized.